Preheat oven to 400ºC (200ºC) In Dutch oven or large heavy skillet, heat oil over medium-high heat; cook onions, stirring occasionally, for 5 minutes.

Add red pepper, garlic and fennel seeds; reduce heat to medium and cook for 10 minutes or until onions are very soft and golden. Transfer to bowl. Cut sausage into 1-inch (2.5 cm) chunks; add to pan and brown well on all sides, about 8 minutes Drain off fat. Stir in pasta sauce and vinegar.

Return vegetable mixture to pan; reduce heat to medium-low and simmer for 15 minutes. Meanwhile, in large pot of boiling salted water, cook pasta for about 8 minutes or until tender but firm.

Drain, reserving 1 cup (250 mL) of the cooking water. Return pasta to pot; add sauce and reserved cooking water. Combine mozzarella and Parmesan cheese; set 1 cup (250 mL) aside. Stir remaining cheese into pasta mixture.

Pour into 13 x 9-inch (3 L) glass baking dish, pressing pasta to submerge. Sprinkle with reserved cheese and parsley. Bake, covered, in oven for 30 to 45 minutes; uncover and continue for another 15 minutes or until golden.